French Pat. No. 2,442,219 describes a method and apparatus for bending or bending and tempering glass sheets by passing the sheets over a bed of curved rollers or rods placed along a curved profile. Such apparatus heats the glass sheets to their softening temperature and passes the sheets over a bed of curved rollers so that as the glass sheets advance over the rollers they acquire a curvature in their direction of movement conforming to the shape of the bed of curved rollers. In addition, the sheets will also acquire the same transverse curvature as that of the rollers or rods over which the advance.
To ensure that the glass sheets pass uniformly over the bed of rollers without abrupt changes in direction, which could adversely affect the quality of the glass, especially at the input to the bending apparatus, the bending apparatus is aligned with the upstream conveyor of the glass sheets so that the sheets undergo only a gradual variation of slope. In apparatus in which glass sheets are given an upwardly concave profile, however, this gradual change in slope results in a very substantial tilt in the end portion of the glass sheet shaping bed. Since the glass sheets will tend to slide at the end portion, it is difficult to handle the sheets properly so that the quality of the sheets is not impaired and the sheets are not damaged.
Additionally, because the point where the glass sheets exit the bending apparatus is typically at a different level from that where the glass sheets enter the bending apparatus, installation difficulties result.
An apparatus which bends sheets of glass so that the sheets become concave upwardly has the advantage of being able to apply glass coatings to the surface of the sheets which is not in contact with the support rollers. These coatings may be fragile as, for example, layers or strips of enamel that have not yet solidified after vitrification occurring during heating of the glass sheets in preparation for bending and tempering. If the glass sheets to be introduced into the glass bending and tempering apparatus are to be used for windshields, back windows, or side windows of motor vehicles, such strips of enamel are typically placed on the periphery of the glass sheet to mask the glue used to attach the glass sheets and to obtain a clean, uniform appearance.